Chlorine-based hardmask removal

ABSTRACT

A method of removing titanium nitride hardmask is described. The hardmask resides above a low-k dielectric layer prior to removal and the low-k dielectric layer retains a relatively low net dielectric constant after the removal process. The low-k dielectric layer may be part of a dual damascene structure having copper at the bottom of the vias. A non-porous carbon layer is deposited prior to the titanium nitride hardmask removal to protect the low-k dielectric layer and the copper. The titanium nitride hardmask is removed with a gas-phase etch using plasma effluents formed in a remote plasma from a chlorine-containing precursor. Plasma effluents within the remote plasma are flowed into a substrate processing region where the plasma effluents react with the titanium nitride.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Prov. Pat. App. No.62/054,913 filed Sep. 24, 2014, and titled “SELECTIVE DRY ETCH PROCESS”by Pandit et al., which is hereby incorporated herein in its entirety byreference for all purposes. This application also claims the benefit ofU.S. Prov. Pat. App. No. 62/055,218 filed Sep. 25, 2014, and titled“METHOD OF TIN HARDMASK REMOVAL FOR COPPER/LOW-K DUAL DAMASCENE DEVICES”by Pandit et al., which is hereby incorporated herein in its entirety byreference for all purposes.

FIELD

Embodiments of the invention relate to removing hardmasks.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a pattern in photoresist into underlyinglayers, thinning layers or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess which etches one material faster than another helping e.g. apattern transfer process proceed. Such an etch process is said to beselective of the first material relative to the second material. As aresult of the diversity of materials, circuits and processes, etchprocesses have been developed with a selectivity towards a variety ofmaterials.

Dry etch processes are often desirable for selectively removing materialfrom semiconductor substrates. The desirability stems from the abilityto gently remove material from miniature structures with minimalphysical disturbance. Dry etch processes also allow the etch rate to beabruptly stopped by removing the gas phase reagents. Some dry-etchprocesses involve the exposure of a substrate to remote plasmaby-products formed from one or more precursors to achieve high etchselectivity. The high selectivities achieved enable novel processsequences.

Methods are needed to broaden the process sequences which take advantageof the high etch selectivities afforded by these novel remote plasma dryetch processes.

SUMMARY

A method of removing titanium nitride hardmask is described. Thehardmask resides above a low-k dielectric layer prior to removal and thelow-k dielectric layer retains a relatively low net dielectric constantafter the removal process. The low-k dielectric layer may be part of adual damascene structure having copper at the bottom of the vias. Anon-porous carbon layer is deposited prior to the titanium nitridehardmask removal to protect the low-k dielectric layer and the copper.The titanium nitride hardmask is removed with a gas-phase etch usingplasma effluents formed in a remote plasma from a chlorine-containingprecursor. Plasma effluents within the remote plasma are flowed into asubstrate processing region where the plasma effluents react with thetitanium nitride.

Embodiments of the invention include methods of removing titaniumnitride hardmasks. The methods include forming a carbon-containing layerover low-k dielectric walls over an underlying copper layer on apatterned substrate. The low-k dielectric walls form a gap and thepatterned substrate further includes titanium nitride hardmasks abovethe low-k dielectric walls. One of the titanium nitride hardmasks iswider than an underlying supporting low-k dielectric wall. The methodsfurther include etching the carbon-containing layer to expose thetitanium nitride hardmasks leaving behind a remainder of thecarbon-containing layer. The methods further include placing thepatterned substrate in a substrate processing region of a substrateprocessing chamber. The methods further include flowing achlorine-containing precursor into a remote plasma region fluidlycoupled to the substrate processing region while forming a remote plasmain the remote plasma region to produce plasma effluents. The methodsfurther include flowing the plasma effluents into the substrateprocessing region through through-holes in a showerhead disposed betweenthe substrate processing region and the remote plasma region. Themethods further include forming a local plasma in the substrateprocessing region to further excite the plasma effluents. The methodsfurther include etching the titanium nitride hardmasks with the plasmaeffluents. The plasma effluents do not react with the underlying copperlayer as a result of a presence of the remainder of thecarbon-containing layer. The methods further include removing theremainder of the carbon-containing layer.

Embodiments of the invention include methods of removing titaniumnitride hardmasks. The methods include forming a carbon-containing layerover low-k dielectric walls over an underlying copper layer on apatterned substrate. The low-k dielectric walls form a trench and a viafluidly coupled to one another and the low-k dielectric walls are cappedwith titanium nitride hardmasks. The titanium nitride hardmasks overhangthe low-k dielectric walls. The methods further include dry-etching thecarbon-containing layer to expose the titanium nitride hardmasks leavingbehind a remainder of the carbon-containing layer. The methods furtherinclude placing the patterned substrate in a substrate processing regionof a substrate processing chamber. The methods further include flowing aradical-chlorine precursor into the substrate processing region. Theradical-chlorine precursor is prevented from reacting with theunderlying copper layer by the remainder of the carbon-containing layer.The methods further include etching away the titanium nitride hardmasks.The methods further include removing the remainder of thecarbon-containing layer.

Embodiments of the invention include methods of removing a hardmask. Themethods include forming a conformal amorphous carbon-containing layerover a patterned substrate. The patterned substrate includes a trenchand a via below the trench. The via is above an underlying copper layer.Sidewalls of the trench and the via include low-k dielectric walls andthe sidewalls of the trench further include the hardmask comprisingtitanium nitride features. The titanium nitride features form a narrowergap at the top of the trench than a width of the trench between thelow-k dielectric walls. The trench is fluidly coupled to the via. Themethods further include etching back the conformal amorphouscarbon-containing layer to expose the titanium nitride features leavingbehind a remainder of the conformal amorphous carbon-containing layer.The remainder of the conformal amorphous carbon-containing layercompletely covers both the underlying copper layer and the low-kdielectric walls so reactants cannot reach either the underlying copperlayer or the low-k dielectric walls. The methods further includeremoving the titanium nitride features. The methods further includeremoving the remainder of the conformal amorphous carbon-containinglayer.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosed embodiments. The features andadvantages of the disclosed embodiments may be realized and attained bymeans of the instrumentalities, combinations, and methods described inthe specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodimentsmay be realized by reference to the remaining portions of thespecification and the drawings.

FIG. 1 is a flow chart of a titanium nitride hardmask removal processaccording to embodiments.

FIGS. 2A, 2B, 2C, 2D and 2E show cross-sectional views of a device atstages of a titanium nitride hardmask removal process according toembodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a portion of asubstrate processing chamber according to embodiments.

FIG. 3C shows a bottom view of a showerhead according to embodiments.

FIG. 4 shows a top view of an exemplary substrate processing systemaccording to embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

A method of removing titanium nitride hardmask is described. Thehardmask resides above a low-k dielectric layer prior to removal and thelow-k dielectric layer retains a relatively low net dielectric constantafter the removal process. The low-k dielectric layer may be part of adual damascene structure having copper at the bottom of the vias. Anon-porous carbon layer is deposited prior to the titanium nitridehardmask removal to protect the low-k dielectric layer and the copper.The titanium nitride hardmask is removed with a gas-phase etch usingplasma effluents formed in a remote plasma from a chlorine-containingprecursor. Plasma effluents within the remote plasma are flowed into asubstrate processing region where the plasma effluents react with thetitanium nitride.

Copper dual-damascene structures have been used for several decades andinclude two distinct patterns formed into a dielectric layer. The lowerpattern may include via structures whereas the upper pattern may includea trench. The via and the trench are filled at the same time which isthe operation for which the dual-damascene process gets its name. Atitanium nitride hardmask may be used for one or both of the patterningoperations (the via and/or the trench). The removal of the titaniumnitride hardmask is accomplished herein in a manner from the methodsused previously. Past methods include removing the titanium nitridehardmask using chemical mechanical polishing but the overhang of thetitanium nitride hardmask has already compromised the copper filling ofthe via/trench. Past methods further include removing the titaniumnitride using the SC1 cleaning solution prior to copper filling but theSC1 solution can damage the exposed copper at the bottom of the via. Themethods presented herein avoid both of these issues.

In order to better understand and appreciate the invention, reference isnow made to FIG. 1 which is a titanium nitride hardmask removal process101 according to embodiments. Concurrently, reference will be made toFIGS. 2A, 2B, 2C, 2D and 2E which show cross-sectional views of a deviceat various stages of titanium nitride hardmask removal process 101. Theportion of the device shown may be a back-end of the line (BEOL)interconnect portion of an integrated circuit during formation inembodiments. Prior to the first operation (FIG. 2A), an exposed titaniumnitride layer is formed, patterned into titanium nitride hardmask 230,and used to pattern an underlying low-k dielectric layer 220 on thepatterned substrate. Silicon carbon nitride layer 210 may be used tophysically separate underlying copper layer 201 from low-k dielectriclayer 220. Underlying copper layer 201 is located beneath the low-kdielectric layer and is exposed to the atmosphere through via andtrench. Titanium nitride hardmask 230 may be physically separated fromlow-k dielectric layer 220 by an auxiliary hardmask to facilitateprocessing, though no such layer is shown in FIG. 2. The auxiliaryhardmask layer may be a silicon oxide hardmask in embodiments. “Top”,“above” and “up” will be used herein to describe portions/directionsperpendicularly distal from the substrate plane and further away fromthe center of mass of the substrate in the perpendicular direction.“Vertical” will be used to describe items aligned in the “up” directiontowards the “top”. Other similar terms may be used whose meanings willnow be clear.

A carbon-containing layer 240-1 is formed on the patterned substrate inoperation 110, shown following formation in FIG. 2B. Thecarbon-containing layer may be nonconformal or conformal on the featuresof patterned substrate in embodiments. The carbon-containing layer maymostly fill gaps or completely fill gaps (as shown in FIG. 2B) in thelow-k dielectric layer of the patterned substrate including the viaand/or the trench in the example of FIGS. 1-2. Carbon-containing layer240-1 may be an amorphous carbon gapfill carbon-containing layer 240-1having a higher density and lower porosity than, for example, organiccarbon-containing layers in embodiments. The carbon-containing layer mayinhibit diffusion of subsequently-introduced etchants and may thereforeprotect the integrity of low-k dielectric layer 220 and underlyingcopper layer 201 during processing. A silicon carbon nitride layer 210may be positioned between underlying copper layer 201 and low-kdielectric layer 220 as shown in FIG. 2A. Organic carbon-containinglayers have been found to allow diffusion of etchants which increase theeffective dielectric constant of low-k dielectric layer 220 and corrodeunderlying copper layer 201. Organic carbon-containing layers, such asorganic planarization layers, retain chemical bonding geometries presentin organic molecules and therefore allow diffusion whencarbon-containing layer 240-1 inhibits or stops diffusion inembodiments. The carbon-containing layer may comprise or consist only ofcarbon, hydrogen and nitrogen in embodiments.

Carbon-containing layer 240-1 is etched back to expose titanium nitridehardmask 230 in operation 120, shown following the operation in FIG. 2C.Etching operation 120 may be anisotropic or isotropic according toembodiments. Etching operation 120 may involve remote and/or locallyexcited etchants formed from halogen-containing and/or oxygen-containingprecursors. Oxygen-containing precursors may be used to etch backcarbon-containing layer 240-1, however, enough carbon-containing layer240-2 should be retained to completely seal low-k dielectric layer 220in embodiments. Sealing low-k dielectric layer 220 withcarbon-containing layer 240-2 avoids any excessive increase indielectric constant for low-k dielectric layer 220 in subsequentprocessing. Halogen-containing precursors may be used to etch backcarbon-containing layer 240-1, according to embodiments, and the plasmas(local and/or remote) may be devoid of oxygen during operation 120.

A flow of chlorine (Cl₂) is introduced into a plasma region separatefrom the processing region (operation 130). Other sources of chlorinemay be used to augment or replace the chlorine. In general, achlorine-containing precursor may be flowed into the plasma region, suchas diatomic chlorine (Cl₂), atomic chlorine, xenon dichloride or borontrichloride. The separate plasma region may be referred to as a remoteplasma region herein and may be within a distinct module from theprocessing chamber or a compartment within the processing chamber. Acarbon-and-hydrogen-containing precursor, such as methane, may also beflowed into the plasma region excited along with the chlorine. Thecarbon-and-hydrogen-containing precursor is optional and includedprimarily to help remove titanium oxide which is often present as a thinoxidation layer on the surface of the titanium nitride.

The plasma effluents formed in the remote plasma region are flowed intothe substrate processing region (in operation 130 as well). Titaniumnitride hardmask 230 on the substrate is selectively etched (operation140) such that titanium nitride hardmask 230 may be removed more rapidlythan a variety of other materials. FIG. 2D shows the patterned substratefollowing operation 140. Operation 140 may involve removal or completeremoval of the titanium nitride hardmasks in embodiments. The selectiveetch of all examples disclosed herein may etch titanium nitridesignificantly faster than a variety of titanium-free dielectricmaterials which may include hafnium oxide (HfO₂) or a silicon-containingmaterial such as silicon (e.g. polysilicon), silicon oxide, low-Kdielectric, silicon nitride or silicon carbon nitride accordingembodiments. Such a process may have broad-based utility, for example,the etch processes disclosed herein may be used to selectively removetitanium nitride from atop a silicon-containing film stack afterpatterning. Carbon-containing layer 240-1 may be removed at this point(in operation 150) since the protection afforded by carbon-containinglayer 240-1 may no longer be necessary at this point in the process.FIG. 2E shows the patterned substrate following operation 150.

The titanium nitride etch selectivity of the processes disclosed hereinmay be greater than or about 10:1, greater than or about 20:1, greaterthan or about 50:1, or greater than or about 100:1 for materials otherthan titanium nitride in embodiments. Applying a bias power, but keepingthe level low as recited shortly, may increase these already-elevatedselectivities. The processes disclosed herein display etch selectivitiesof titanium nitride relative to a variety of specific materials. Inpractice, under conditions of low bias power in the substrate processingregion local plasma, etch rates of many of these materials were so lowas to be not accurately measurable. The etch selectivity of titaniumnitride relative to silicon oxide may be greater than or about 100:1,greater than or about 250:1, greater than or about 500:1 or greater thanor about 1000:1 in embodiments. Silicon oxide may be used as a hardmasklayer between low-k dielectric layer 220 and titanium nitride hardmask230. Low-k dielectric films and silicon carbon nitride films, such asBlack Diamond III™ and Blok™ (both available from Applied Materials),respectively, displayed essentially unmeasurable etch rates. The etchselectivity of titanium nitride relative to silicon oxycarbide (e.g.Black Diamond III™) may be greater than or about 100:1, greater than orabout 250:1, greater than or about 500:1 or greater than or about 1000:1in embodiments. The etch selectivity of titanium nitride relative tosilicon carbon nitride (e.g. Blok™) may be greater than or about 100:1,greater than or about 250:1, greater than or about 500:1 or greater thanor about 1000:1 according to embodiments.

The trench structures filled with the carbon-containing layer may be adual-damascene structure including a via underlying a trench. The viamay be a low aspect ratio gap and may be, e.g., circular as viewed fromabove the patterned substrate laying flat. The structure may be at theback end of the line which may result in larger dimensions depending onthe device type. A width of the via may be less than 50 nm, less than 40nm, less than 30 nm or less than 20 nm according to embodiments. A widthof the trench may be less than 70 nm, less than 50 nm, less than 40 nmor less than 30 nm in embodiments. The dimensions described herein applyto a dual-damascene structure or structures involving a single layer. Anaspect ratio of the via may be about 1:1, as viewed from above, whereasan aspect ratio of the trench may be greater than 10:1 since the trenchis used to contain a conductor meant to electrically attach multiplevias.

The carbon-and-hydrogen-containing precursor is included primarily tohelp remove the titanium oxide layer from atop the titanium nitridelayer. The carbon-and-hydrogen-containing precursor may be methane (CH₄)as in the example, but may also be a higher order hydrocarbon such asethane (C₂H₆). In general, the carbon-and-hydrogen-containing precursormay include carbon and hydrogen and may consist only of carbon andhydrogen. The carbon-and-hydrogen-containing precursor may contain onlysingle bonds in embodiments. A hydrocarbon with some multiple bonds maybe used and hydrogen (H₂) may be added to the remote plasma region aswell, during the process, in order to adjust the H:C atomic flow ratio.

The flows of the chlorine-containing precursor and optionalcarbon-and-hydrogen-containing precursor may further include one or morerelatively inert gases such as He, N₂, Ar. The inert gas can be used toimprove plasma stability or process uniformity. Argon is helpful, as anadditive, to promote the formation of a stable plasma. Processuniformity is generally increased when helium is included. Theseadditives are present in embodiments throughout this specification. Flowrates and ratios of the different gases may be used to control etchrates and etch selectivity.

In embodiments, the chlorine-containing precursor (e.g. Cl₂) is suppliedat a flow rate of between about 25 sccm (standard cubic centimeters perminute) and 800 sccm, the carbon-and-hydrogen-containing precursor (e.g.CH₄) at a flow rate of between about 50 sccm and 600 sccm, He at a flowrate of between about 0 slm (standard liters per minute) and 3 slm, andAr at a flow rate of between about 0 slm and 3 slm. One of ordinaryskill in the art would recognize that other gases and/or flows may beused depending on a number of factors including processing chamberconfiguration, substrate size, geometry and layout of features beingetched.

During etching process 140, the substrate may be maintained may bebetween about −30° C. and about 400° C. in general. The temperature ofthe patterned substrate during etching operation 140 may be between −20°C. and 350° C., −10° C. and −250° C., between 0° C. and 50° C. orbetween 5° C. and 20° C. in embodiments. The pressure in the substrateprocessing region and the remote plasma region(s) during etchingoperation 140 may be between 0.1 Torr and 50 Torr, between 1 Torr and 15Torr or between 5 Torr and 10 Torr in embodiments. By maintaining thesubstrate temperature relatively low, such as below 10° C., andmaintaining the process chamber at a pressure below 10 Torr, the etchselectivity may be enhanced through the suppression of the etch rate ofthe materials other than titanium nitride.

The method also includes applying energy to the chlorine-containingprecursor and the optional carbon-and-hydrogen-containing precursor(CH₄) while they are in the remote plasma region to generate the plasmaeffluents. As would be appreciated by one of ordinary skill in the art,the plasma may include a number of charged and neutral species includingradicals and ions. The plasma in the remote plasma region (e.g. in thechamber plasma region) may be generated using known techniques (e.g.,radio frequency excitations, capacitively-coupled power, inductivelycoupled power, etc.). In an embodiment, the energy is applied using acapacitively-coupled plasma unit. The remote plasma source power may bebetween about 40 watts and about 1500 watts, between about 100 watts andabout 1200 watts, between about 250 watts and about 1000 watts, orbetween about 400 watts and about 800 watts in embodiments. The 400 wattto 800 watt range may optimize the selective removal of titanium nitriderelative to a variety of other exposed materials includingsilicon-containing dielectric films as well as some metals and metaloxides which do not contain titanium. The capacitively-coupled plasmaunit may be disposed remote from the substrate processing region butstill within the substrate processing chamber. For example, thecapacitively-coupled plasma unit and the plasma generation region may beseparated from the gas reaction region by a showerhead. Alternatively,The remote plasma power may be applied to the remote plasma region at alevel between 500 W and 10 kW for a remote plasma external to thesubstrate processing chamber. The remote plasma power may be appliedusing inductive coils, in embodiments, in which case the remote plasmawill be referred to as an inductively-coupled plasma (ICP).

Plasma power may also be simultaneously applied to both the remoteplasma region (e.g. the chamber plasma region) and substrate processingregion during etching processes described herein. The plasma in thechamber plasma region may have a higher power applied in order to createa high concentration of neutral radicals entering substrate processingregion. The plasma power applied to substrate processing region may belower in order to not unduly increase the ionic concentration near thesubstrate. However, the local plasma in the substrate processing regionmay be biased relative to the substrate in order to apply a sputteringcomponent. A sputtering component of the local plasma may be includedprimarily to remove titanium oxide which may cover the titanium nitrideto be etched. The plasma in the substrate processing region may bereferred to herein as a local plasma because it resides nearest thesubstrate and within the substrate processing region. The local plasmamay be generated using the same techniques used to create the remoteplasma. As with the remote plasma, the energy may be applied using acapacitively-coupled plasma unit by applying RF power between platesabove and below the substrate during etching. The local plasma RF powermay be between about 5 watts and about 200 watts, between about 10 wattsand about 150 watts, between about 15 watts and about 100 watts, orbetween about 20 watts and about 80 watts in embodiments. The lowerlocal RF power of the local plasma in the substrate processing regionkeeps the ionic concentration down so the etch selectivity towardtitanium nitride remains high. The local plasma RF power may be lessthan or about 20% of the remote plasma RF power, less than or about 15%of the remote plasma RF power, or less than or about 10% of the remoteplasma RF power.

The local plasma is used, in embodiments, to facilitate removal of atitanium oxide layer which may be on top of the titanium nitride layer.The local plasma may be biased relative to the substrate to furtherassist removal of any titanium oxide layer by using a physicalsputtering mechanism in addition to the chemical mechanism. Titaniumoxide may require the sputtering assistance because the bonding isstronger in titanium oxide than in titanium nitride. The local plasmabias RF power may be between about 2 watts and about 100 watts, betweenabout 3 watts and about 75 watts, between about 5 watts and about 60watts, or between about 10 watts and about 50 watts in embodiments. Thelocal plasma bias RF power is not included in the local plasma RF powerso the total applied RF power is the sum of these two quantities.

Despite the optional use of local plasma excitation, an ion suppressor(which may be the showerhead) may be used to provide radical and/orneutral species for gas-phase etching. The ion suppressor may also bereferred to as an ion suppression element. In embodiments, for example,the ion suppressor is used to filter etching plasma effluents en routefrom the remote plasma region to the substrate processing region. Theion suppressor may be used to provide a reactive gas having a higherconcentration of radicals than ions. Plasma effluents pass through theion suppressor disposed between the remote plasma region and thesubstrate processing region. The ion suppressor functions todramatically reduce or substantially eliminate ionic species travelingfrom the plasma generation region to the substrate. The ion suppressorsdescribed herein are simply one way to achieve a low electrontemperature in the substrate processing region during the gas-phase etchprocesses described herein.

In embodiments, an electron beam is passed through the substrateprocessing region in a plane parallel to the substrate to reduce theelectron temperature of the plasma effluents. A simpler showerhead maybe used if an electron beam is applied in this manner. The electron beammay be passed as a laminar sheet disposed above the substrate inembodiments. The electron beam provides a source of neutralizingnegative charge and provides a more active means for reducing the flowof positively charged ions towards the substrate and increasing the etchselectivity in embodiments. The flow of plasma effluents and variousparameters governing the operation of the electron beam may be adjustedto lower the electron temperature measured in the substrate processingregion.

The electron temperature may be measured using a Langmuir probe in thesubstrate processing region during excitation of a plasma in the remoteplasma. In aluminum removal embodiments, the electron temperature may beless than 0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35eV. These extremely low values for the electron temperature are enabledby the presence of the electron beam, showerhead and/or the ionsuppressor. Uncharged neutral and radical species may pass through theelectron beam and/or the openings in the ion suppressor to react at thesubstrate. Such a process using radicals and other neutral species canreduce plasma damage compared to conventional plasma etch processes thatinclude sputtering and bombardment. Embodiments of the present inventionare also advantageous over conventional wet etch processes where surfacetension of liquids can cause bending and peeling of small features. Inpoint of contrast, the electron temperature during the aluminum oxideremoval process may be greater than 0.5 eV, greater than 0.6 eV orgreater than 0.7 eV according to embodiments.

The substrate processing region may be described herein as “plasma-free”during the etch processes described herein. “Plasma-free” does notnecessarily mean the region is devoid of plasma. Ionized species andfree electrons created within the plasma region may travel through pores(apertures) in the partition (showerhead) at exceedingly smallconcentrations. The borders of the plasma in the chamber plasma regionmay encroach to some small degree upon the substrate processing regionthrough the apertures in the showerhead. Furthermore, a low intensityplasma may be created in the substrate processing region withouteliminating desirable features of the etch processes described herein.All causes for a plasma having much lower intensity ion density than thechamber plasma region during the creation of the excited plasmaeffluents do not deviate from the scope of “plasma-free” as used herein.

The examples described herein involve the preparation of a long trenchabove a low-aspect ratio via in a dual-damascene structure. Generallyspeaking the structure may involve only one level and the low-kdielectric layer may have a long trench and/or a low-aspect ratio viaaccording to embodiments. For the purposes of description herein andclaim recitations below, a via is simply a low-aspect ratio trench andso the term “trench” covers all holes in a low-k dielectric describedherein. The use of carbon-containing layer 240 avoids the requirement ofleaving a portion of silicon carbon nitride layer 210 at the bottom ofthe trench to protect underlying copper layer 201. A low-temperatureoxide (LTO) was used instead of carbon-containing layer 240 and thelow-k structures distorted and collapsed. Using carbon-containing layer240 to protect low-k dielectric layer 220 and underlying copper layer201 may avoid distorting and ruining low-k structures according toembodiments. Generally speaking, underlying copper layer 201 may be anyunderlying conducting layer in embodiments. Following operation 150, thetrench and the via may be filled with a conductor (e.g. copper) tocomplete the dual-damascene portion of a semiconductor manufacturingprocess.

FIG. 3A shows a cross-sectional view of an exemplary substrateprocessing chamber 1001 with a partitioned plasma generation regionwithin the processing chamber. During film etching, a process gas may beflowed into chamber plasma region 1015 through a gas inlet assembly1005. A remote plasma system (RPS) 1002 may optionally be included inthe system, and may process a first gas which then travels through gasinlet assembly 1005. The process gas may be excited within RPS 1002prior to entering chamber plasma region 1015. Accordingly, thechlorine-containing precursor as discussed above, for example, may passthrough RPS 1002 or bypass the RPS unit in embodiments.

A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead1025, and a substrate support 1065 (also known as a pedestal), having asubstrate 1055 disposed thereon, are shown and may each be includedaccording to embodiments. Pedestal 1065 may have a heat exchange channelthrough which a heat exchange fluid flows to control the temperature ofthe substrate. This configuration may allow the substrate 1055temperature to be cooled or heated to maintain relatively lowtemperatures, such as between −20° C. to 200° C. Pedestal 1065 may alsobe resistively heated to relatively high temperatures, such as between100° C. and 1100° C., using an embedded heater element.

Exemplary configurations may include having the gas inlet assembly 1005open into a gas supply region 1058 partitioned from the chamber plasmaregion 1015 by faceplate 1017 so that the gases/species flow through theholes in the faceplate 1017 into the chamber plasma region 1015.Structural and operational features may be selected to preventsignificant backflow of plasma from the chamber plasma region 1015 backinto the supply region 1058, gas inlet assembly 1005, and fluid supplysystem 1010. The structural features may include the selection ofdimensions and cross-sectional geometries of the apertures in faceplate1017 to deactivate back-streaming plasma. The operational features mayinclude maintaining a pressure difference between the gas supply region1058 and chamber plasma region 1015 that maintains a unidirectional flowof plasma through the showerhead 1025. The faceplate 1017, or aconductive top portion of the chamber, and showerhead 1025 are shownwith an insulating ring 1020 located between the features, which allowsan AC potential to be applied to the faceplate 1017 relative toshowerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 maybe positioned between the faceplate 1017 and the showerhead 1025 and/orion suppressor 1023 enabling a capacitively coupled plasma (CCP) to beformed in the chamber plasma region.

The plurality of holes in the ion suppressor 1023 may be configured tocontrol the passage of the activated gas, i.e., the ionic, radical,and/or neutral species, through the ion suppressor 1023. For example,the aspect ratio of the holes, or the hole diameter to length, and/orthe geometry of the holes may be controlled so that the flow ofionically-charged species in the activated gas passing through the ionsuppressor 1023 is reduced. The holes in the ion suppressor 1023 mayinclude a tapered portion that faces chamber plasma region 1015, and acylindrical portion that faces the showerhead 1025. The cylindricalportion may be shaped and dimensioned to control the flow of ionicspecies passing to the showerhead 1025. An adjustable electrical biasmay also be applied to the ion suppressor 1023 as an additional means tocontrol the flow of ionic species through the suppressor. The ionsuppression element 1023 may function to reduce or eliminate the amountof ionically charged species traveling from the plasma generation regionto the substrate. Uncharged neutral and radical species may still passthrough the openings in the ion suppressor to react with the substrate.

Plasma power can be of a variety of frequencies or a combination ofmultiple frequencies. In the exemplary processing system the plasma maybe provided by RF power delivered to faceplate 1017 relative to ionsuppressor 1023 and/or showerhead 1025. The RF power may be betweenabout 10 watts and about 5000 watts, between about 100 watts and about2000 watts, between about 200 watts and about 1500 watts, or betweenabout 200 watts and about 1000 watts in embodiments. The RF frequencyapplied in the exemplary processing system may be low RF frequenciesless than about 200 kHz, high RF frequencies between about 10 MHz andabout 15 MHz, or microwave frequencies greater than or about 1 GHz inembodiments. The plasma power may be capacitively-coupled (CCP) orinductively-coupled (ICP) into the remote plasma region.

A precursor, for example a chlorine-containing precursor and acarbon-and-hydrogen-containing precursor, may be flowed into substrateprocessing region 1033 by embodiments of the showerhead describedherein. Excited species derived from the process gas in chamber plasmaregion 1015 may travel through apertures in the ion suppressor 1023,and/or showerhead 1025 and react with an additional precursor flowinginto substrate processing region 1033 from a separate portion of theshowerhead. Alternatively, if all precursor species are being excited inchamber plasma region 1015, no additional precursors may be flowedthrough the separate portion of the showerhead. Little or no plasma maybe present in substrate processing region 1033 during the remote plasmaetch process. Excited derivatives of the precursors may combine in theregion above the substrate and/or on the substrate to etch structures orremove species from the substrate.

The processing gases may be excited in chamber plasma region 1015 andmay be passed through the showerhead 1025 to substrate processing region1033 in the excited state. A local plasma may be formed in substrateprocessing region 1033 concurrently with the remote plasma in thechamber plasma region 1015 as described previously. Alternatively, aplasma may not be generated in substrate processing region 1033 inembodiments.

FIG. 3B shows a detailed view of the features affecting the processinggas distribution through faceplate 1017. The gas distribution assembliessuch as showerhead 1025 for use in the processing chamber section 1001may be referred to as dual channel showerheads (DCSH) and areadditionally detailed in the embodiments described in FIG. 3A as well asFIG. 3C herein. The dual channel showerhead may provide for etchingprocesses that allow for separation of etchants outside of theprocessing region 1033 to provide limited interaction with chambercomponents and each other prior to being delivered into the processingregion.

The showerhead 1025 may comprise an upper plate 1014 and a lower plate1016. The plates may be coupled with one another to define a volume 1018between the plates. The coupling of the plates may be so as to providefirst fluid channels 1019 through the upper and lower plates, and secondfluid channels 1021 through the lower plate 1016. The formed channelsmay be configured to provide fluid access from the volume 1018 throughthe lower plate 1016 by way of second fluid channels 1021 alone, and thefirst fluid channels 1019 may be fluidly isolated from the volume 1018between the plates and the second fluid channels 1021. The volume 1018may be fluidly accessible through a side of the gas distributionassembly 1025. Although the exemplary system of FIGS. 3A-3C includes adual-channel showerhead, it is understood that alternative distributionassemblies may be utilized that maintain first and second precursorsfluidly isolated prior to substrate processing region 1033. For example,a perforated plate and tubes underneath the plate may be utilized,although other configurations may operate with reduced efficiency or notprovide as uniform processing as the dual-channel showerhead described.

In the embodiment shown, showerhead 1025 may distribute by way of firstfluid channels 1019 process gases which contain plasma effluents uponexcitation by a plasma in chamber plasma region 1015. In embodiments,the process gas introduced into RPS 1002 and/or chamber plasma region1015 may contain chlorine, e.g., Cl₂ and possibly acarbon-and-hydrogen-containing precursor such as CH₄. The process gasmay also include a carrier gas such as helium, argon, nitrogen (N₂),etc. Plasma effluents may include ionized or neutral derivatives of theprocess gas and may also be referred to herein as a radical-chlorineprecursor referring to the atomic constituent of the process gasintroduced.

FIG. 3C is a bottom view of a showerhead 1025 for use with a processingchamber in embodiments. Showerhead 1025 corresponds with the showerheadshown in FIG. 3A. Through-holes 1031, which show a view of first fluidchannels 1019, may have a plurality of shapes and configurations tocontrol and affect the flow of precursors through the showerhead 1025.Small holes 1027, which show a view of second fluid channels 1021, maybe distributed substantially evenly over the surface of the showerhead,even amongst the through-holes 1031, which may help to provide more evenmixing of the precursors as they exit the showerhead than otherconfigurations.

Embodiments of the dry etch systems may be incorporated into largerfabrication systems for producing integrated circuit chips. FIG. 4 showsone such processing system (mainframe) 1101 of deposition, etching,baking, and curing chambers in embodiments. In the figure, a pair offront opening unified pods (load lock chambers 1102) supply substratesof a variety of sizes that are received by robotic arms 1104 and placedinto a low pressure holding area 1106 before being placed into one ofthe substrate processing chambers 1108 a-f. A second robotic arm 1110may be used to transport the substrate wafers from the holding area 1106to the substrate processing chambers 1108 a-f and back. Each substrateprocessing chamber 1108 a-f, can be outfitted to perform a number ofsubstrate processing operations including the dry etch processesdescribed herein in addition to cyclical layer deposition (CLD), atomiclayer deposition (ALD), chemical vapor deposition (CVD), physical vapordeposition (PVD), etch, pre-clean, degas, orientation, and othersubstrate processes.

The showerhead may be referred to as a dual-channel showerhead as aresult of the two distinct pathways into the substrate processingregion. The chlorine-containing precursor and thecarbon-and-hydrogen-containing precursor may be flowed through thethrough-holes in the dual-zone showerhead and auxiliary precursors maypass through separate zones in the dual-zone showerhead. The separatezones may open into the substrate processing region but not into theremote plasma region as described above.

Combined flow rates of water vapor and plasma effluents into thesubstrate processing region may account for 0.05% to about 20% by volumeof the overall gas mixture; the remainder being carrier gases. Thechlorine-containing precursor and the carbon-and-hydrogen-containingprecursor flowed into the remote plasma region but the plasma effluentshas the same volumetric flow ratio, in embodiments. In the case of thechlorine-containing precursor, a purge or carrier gas may be firstinitiated into the remote plasma region before those of thechlorine-containing gas and the carbon-and-hydrogen-containing precursorto stabilize the pressure within the remote plasma region.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon oxide” of thepatterned substrate is predominantly SiO₂ but may include concentrationsof other elemental constituents such as, e.g., nitrogen, hydrogen andcarbon. In some embodiments, silicon oxide portions etched using themethods disclosed herein consist essentially of silicon and oxygen.Exposed “silicon nitride” of the patterned substrate is predominantlySi₃N₄ but may include concentrations of other elemental constituentssuch as, e.g., oxygen, hydrogen and carbon. In some embodiments, siliconnitride portions described herein consist essentially of silicon andnitrogen. Exposed “titanium nitride” of the patterned substrate ispredominantly titanium and nitrogen but may include concentrations ofother elemental constituents such as, e.g., oxygen, hydrogen and carbon.In some embodiments, titanium nitride portions described herein consistessentially of titanium and nitrogen. The amorphous carbon-containingfilm may include about 79% carbon, 20% hydrogen and 1% nitrogen or maycontain 75-83% carbon, 18%-22% hydrogen and 0.3-2% hydrogen inembodiments. “Copper” of the patterned substrate is predominantly copperbut may include concentrations of other elemental constituents such as,e.g., oxygen, hydrogen and carbon. In some embodiments, copper portionsdescribed herein consist essentially of copper.

The terms “gap” and “trench” are used throughout with no implicationthat the etched geometry has a large horizontal aspect ratio. Viewedfrom above the surface, trenches may appear circular, oval, polygonal,rectangular, or a variety of other shapes. A trench may be in the shapeof a moat around an island of material. The term “via” is used to referto a low aspect ratio trench (as viewed from above) which may or may notbe filled with metal to form a vertical electrical connection. As usedherein, a conformal etch process refers to a generally uniform removalof material on a surface in the same shape as the surface, i.e., thesurface of the etched layer and the pre-etch surface are generallyparallel. A person having ordinary skill in the art will recognize thatthe etched interface likely cannot be 100% conformal and thus the term“generally” allows for acceptable tolerances.

The term “precursor” is used to refer to any process gas which takespart in a reaction to either remove material from or deposit materialonto a surface. “Plasma effluents” describe gas exiting from the chamberplasma region and entering the substrate processing region. Plasmaeffluents are in an “excited state” wherein at least some of the gasmolecules are in vibrationally-excited, dissociated and/or ionizedstates. A “radical precursor” is used to describe plasma effluents (agas in an excited state which is exiting a plasma) which participate ina reaction to either remove material from or deposit material on asurface. “Radical-chlorine precursors” describe radical precursors whichcontain chlorine but may contain other elemental constituents.“Radical-carbon-hydrogen precursors” describe radical precursors whichcontain carbon and hydrogen but may contain other elementalconstituents. The phrase “inert gas” refers to any gas which does notform chemical bonds when etching or being incorporated into a film.Exemplary inert gases include noble gases but may include other gases solong as no chemical bonds are formed when (typically) trace amounts aretrapped in a film.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well-known processesand elements have not been described in order to avoid unnecessarilyobscuring the present invention. Accordingly, the above descriptionshould not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A method of removing titanium nitride hardmasks, the methodcomprising: forming a carbon-containing layer over low-k dielectricwalls over an underlying copper layer on a patterned substrate, whereinthe low-k dielectric walls form a gap and the patterned substratefurther comprises titanium nitride hardmasks above the low-k dielectricwalls, wherein one of the titanium nitride hardmasks is wider than anunderlying supporting low-k dielectric wall; etching thecarbon-containing layer to expose the titanium nitride hardmasks leavingbehind a remainder of the carbon-containing layer; placing the patternedsubstrate in a substrate processing region of a substrate processingchamber; flowing a chlorine-containing precursor into a remote plasmaregion fluidly coupled to the substrate processing region while forminga remote plasma in the remote plasma region to produce plasma effluents;flowing the plasma effluents into the substrate processing regionthrough through-holes in a showerhead disposed between the substrateprocessing region and the remote plasma region; forming a local plasmain the substrate processing region to further excite the plasmaeffluents; etching the titanium nitride hardmasks with the plasmaeffluents, wherein the plasma effluents do not react with the underlyingcopper layer as a result of a presence of the remainder of thecarbon-containing layer; and removing the remainder of thecarbon-containing layer.
 2. The method of claim 1 wherein the operationof etching the titanium nitride hardmasks removes the titanium nitridehardmasks.
 3. The method of claim 1 wherein the substrate processingregion is plasma-free during the operation of etching the titaniumnitride hardmasks.
 4. The method of claim 1 wherein the operation offlowing the chlorine-containing precursor further comprises flowing acarbon-and-hydrogen-containing precursor into the remote plasma region.5. The method of claim 1 wherein the chlorine-containing precursorcomprises a precursor selected from the group consisting of atomicchlorine, diatomic chlorine, boron trichloride, and xenon dichloride. 6.A method of removing titanium nitride hardmasks, the method comprising:forming a carbon-containing layer over low-k dielectric walls over anunderlying copper layer on a patterned substrate, wherein the low-kdielectric walls form a trench and a via fluidly coupled to one anotherand the low-k dielectric walls are capped with titanium nitridehardmasks, wherein the titanium nitride hardmasks overhang the low-kdielectric walls; dry-etching the carbon-containing layer to expose thetitanium nitride hardmasks leaving behind a remainder of thecarbon-containing layer; placing the patterned substrate in a substrateprocessing region of a substrate processing chamber; flowing aradical-chlorine precursor into the substrate processing region, whereinthe radical-chlorine precursor is prevented from reacting with theunderlying copper layer by the remainder of the carbon-containing layer;etching away the titanium nitride hardmasks; and removing the remainderof the carbon-containing layer.
 7. The method of claim 6 wherein a widthof the via is less than 50 nm.
 8. The method of claim 6 wherein a widthof the trench is less than 70 nm.
 9. The method of claim 6 furthercomprising an operation of filling the via and the trench with copperafter the operation of removing the remainder of the carbon-containinglayer.
 10. The method of claim 6 wherein an electron temperature withinthe substrate processing region is below 0.5 eV during the operation ofetching away the titanium nitride hardmasks.
 11. The method of claim 6wherein a silicon carbon nitride layer is disposed between theunderlying copper layer and at least one of the low-k dielectric walls.12. The method of claim 6 wherein the radical-chlorine precursor isprevented from reacting with the low-k dielectric walls by the remainderof the carbon-containing layer.
 13. The method of claim 6 wherein thecarbon-containing layer consists only of carbon, hydrogen and nitrogen.14. A method of removing a hardmask, the method comprising: forming aconformal amorphous carbon-containing layer over a patterned substrate,wherein the patterned substrate comprises a trench and a via below thetrench, wherein the via is above an underlying copper layer, whereinsidewalls of the trench and the via comprise low-k dielectric walls andthe sidewalls of the trench further comprise the hardmask comprisingtitanium nitride features, wherein the titanium nitride features form anarrower gap at the top of the trench than a width of the trench betweenthe low-k dielectric walls, and wherein the trench is fluidly coupled tothe via; etching back the conformal amorphous carbon-containing layer toexpose the titanium nitride features leaving behind a remainder of theconformal amorphous carbon-containing layer, wherein the remainder ofthe conformal amorphous carbon-containing layer completely covers boththe underlying copper layer and the low-k dielectric walls so reactantscannot reach either the underlying copper layer or the low-k dielectricwalls; removing the titanium nitride features; and removing theremainder of the conformal amorphous carbon-containing layer.
 15. Themethod of claim 14 wherein the hardmask further comprises silicon oxidefeatures underlying the titanium nitride features and overlying thelow-k dielectric walls.